Estimation of roughness coefficients in rivers from flow data

Abstract

    An accurate estimation of Manning's roughness coefficient is of vital importance in any hydraulic study including open channel flows. There are many empirical methods to estimate the values of roughness however these methods are often applicable only to certain conditions. In many rivers, the velocities at two-tenths and eight-tenths of the depth at stations across the river are available. For wide river (ratios between width and depth is appropriate or greater than 10), these data can be used to estimate Manning's roughness n based on a logarithmic velocity distribution.

    This paper re-investigates and improves the method of using two-point velocity measurement to estimate rounghness coefficients to wide rivers. The proposed formulae are applied to 14 rivers in Newzealand and Australia where their roughness coefficients were measured. The results are compared with the measured roughness coefficients and the values computed from some other empirical formulae. It is suggested that this method can be used as a means to estimate roughness coefficients for streams where two-point velocity data are available.